Field of the Invention
The present invention relates to processing for fitting a tube for protecting cables to a gas sensor.
Description of the Background Art
Conventionally, there have been well known gas sensors having sensor elements formed from an oxygen-ion conductive solid electrolyte ceramic, such as zirconia (ZrO2), as devices for determining the concentrations of predetermined gas components in measurement gas, such as combustion gasses and exhaust gasses in internal combustion engines such as automobile engines.
Generally, such a gas sensor interiorly includes a sensor element (detection element) with an elongated plate shape which is made of a ceramic and, also, is structured to be covered, over its outer side, with a member called a cover or a casing. From this cover or the like, cables (connection conductors) for electrically connecting the sensor element to an external drive controller are properly extended outward (refer to International Publication WO 2013/005491 and Japanese Patent No. 4194660).
Such a gas sensor is used in an environment under an atmosphere containing gasses being at higher temperatures and having reactivity and corrosivity or in an environment therearound, such as exhaust ports of internal combustion engines. Therefore, it is necessary to cover the cables with a protection tube having incombustibility, corrosion resistance and the like, in order to prevent the cables from being deformed, deteriorated and corroded due to such an environment. In this case, the protection tube is required to be certainly fitted and secured to the gas sensor.
For example, if a protection tube for covering cables is provided in a gas sensor disclosed in International Publication WO 2013/005491, the protection tube is required to be fitted to an end portion of the gas sensor. Generally, the gas sensor is thicker than the bundle of the cables or both of them have substantially the same thickness and, therefore, it is necessary to expand the tip end portion of the protection tube, in attaining this fitting. In order to prevent the cables from being exposed, it is necessary to prevent the occurrence of cracks and breakages at the tip end portion of the protection tube, in performing this fitting. Further, in order to prevent disengagement of the protection tube, the fitting and securing thereof to the gas sensor should be certainly attained at a predetermined position.
Japanese Patent No. 4194660 discloses a formed hose provided at its end portion with a securing portion to be fitted to a casing of a gas sensor and with a transition portion extending in a conical shape, in an aspect for preventing intrusion of contaminations therein. However, the provision of the securing portion and the conical portion in the formed hose causes an increase of the fabrication cost for the gas sensor.